The present invention relates to a radially expandable assembly drum for the manufacture of tires. The invention relates more particularly to the manufacture of tires comprising a carcass reinforcement, two beads having different diameters, and at least one reinforcing bead wire in each of the beads of the tire within which the carcass reinforcement forms a turnup. However, the invention may also apply to the manufacture of tires which do not have a bead wire but where the beads have different diameters.
It is clear that the production of this type of tire requires the use of an assembly drum which has reception sites for the beads of tires of different diameter. However, this inequality of the diameter of the reception sites causes problems in industrial practice and inadequacies in terms of quality and reliability of the tires so obtained.
In fact, it is important for the quality and reliability of the tire to lay the products constituting the carcass reinforcement, such as plies etc., on the drum in a regular manner both in terms of geometry (centering) and tension in the products. This appears particularly difficult on a drum where the diameters of the reception sites for the beads are different. However, it can be imagined that these difficulties can be overcome by laying the various products by hand slowly and carefully. It is clear that this solution cannot be adapted to an industrial context. Furthermore, the production of the uptum of the carcass reinforcement in the beads of the tire requires tensioning of the carcass reinforcement at the points around which the rotation of said reinforcement will take place, which creates additional difficulties.
Publication EP-0 953 434 describes an assembly drum for manufacturing tires having beads of different diameters. This drum comprises at its ends grooves for receiving the beads, of different diameter and a retractable hoop intended to cover the groove of lesser diameter to present a cylindrical surface for laying the products constituting the carcass reinforcement. Lifting devices located close to the grooves make it possible to turn up the carcass reinforcement when the hoop is in the retracted position. This assembly drum effectively permits production of tires having beads of different diameters; however, the presence of the hoop requires precise adjustment to ensure proper centering relative to the drum, also increases the bulk in particular in terms of length of the latter, making it less accessible, and makes the drum far more mechanically complex.